Guys, I think there is a "timescale" setting (similar to what was available in the Elder Scrolls games if you know what I'm talking about; in those, you needed to open the console and type "set timescale to xx") embedded in RedEngine; infact, a couple mods came out for The Witcher 3 that allowed you to adjust it.
Keep in mind, tho, that, whenever something like that is modified, it is going to create a lot of potential problems with scripted missions, AI behaviours and similar aspects of the game.